docs: def keep_form_with_max_profit(self, forms=None):
          """
          This converts the dataframe, which shows all profitable forms,
          to the form with the greatest profit, so that more profitable
          forms outcompete less profitable forms.
  
          Parameters
          ----------
          forms: list of strings
              List of forms which compete which other.  Can leave some out.
  
          Returns
          -------
          Nothing.  Goes from a multi-index to a single index with only the
          most profitable form.
          """
          f = self.feasibility
  
          if forms is not None:
              f = f[forms]
  
          if len(f) > 0:
              mu = self._max_form(f, "max_profit")
              indexes = [tuple(x) for x in mu.reset_index().values]
          else:
              indexes = []
          df = f.stack(level=0).loc[indexes]
          df.index.names = ["parcel_id", "form"]
          df = df.reset_index(level=1)
          return df